1. Technical Field
The present invention relates to a fitting for coupling a tube to a receiving component and, more particularly, to a fitting wherein rotation effects axial engagement to the component and radial clamping of the tube therein.
2. Background Art
High pressure liquid chromatography (HPLC) systems typically operate at pressures of 5,000 PSI and higher. To withstand these pressures, capillary tubing that connects the various system components is formed from an advanced polymer or plastic or stainless steel. End fittings or couplings are used to tightly clamp, seal and connect the tubing to the HPLC components.
More specifically, end fittings typically have a tubular construction with a through bore sized to receive the capillary tube. The forward end of the fitting typically has an external thread for mechanically connecting the fitting with a cooperating threaded tap of a HPLC component. A separate or integrated tubular ferrule is provided on the fitting forward end.
The fitting has a rearward radially enlarged region suited for finger gripping that allows a user to rotate the fitting without tools with sufficient torque to tighten or loosen it relative to the HPLC component.
When the fitting is tightened into a HPLC component, the forward end ferrule is compressed between the fitting, capillary tube and HPLC component, creating a somewhat small annular region of pressurized ferrule that seals and mechanically clamps the tube and fitting together.
The forces between the ferrule and tube must be substantial in this region as they essentially form the only means axially holding the tube and fitting together. It is not uncommon to have clamping forces on the compressed ferrule that deform the underlying annular region of the tube.
Nonetheless, as this compressed annular ferrule/tube region is small, the generated axial holding force they provide frequently is inadequate at high pressure such that axial tube blowout from the fitting can occur and possibly result in system failure.